A controller, such as a PID controller (Proportional-Integral-Derivative controller) is a control loop feedback mechanism widely used in industrial control systems. Thereby, typically, a controller, in particular a PID controller, may calculate an error value as the difference between a measured process variable (also referred to as system variable) and a desired set-point of the process variable. The controller then attempts to minimize the error by adjusting the process variable through use of a manipulated variable, in particular by feeding or supplying a controller output to the process or system.
The PID controller is characterized by three separate controller parameters, also known as PID-controller parameters. In order to control the system or process appropriately, the PID-controller parameters need to be known in advance. Determining the controller parameters may also be referred to as tuning the three or less controller parameters.
In conventional methods and applications, a manual tuning has been applied or a so-called Ziegler-Nichols method has been applied. However, it has been observed that conventional methods and arrangements for enabling to tune controller parameters may require operator/engineer intervention for a relay tuning test. Often a priori knowledge of relay parameters may be required. Thereby, conventional tuning methods are very cumbersome and time-consuming and may require human intervention.
EP 0530170 (A1) discloses a system for tuning at least one control parameter of a controller in a control loop wherein the system includes an oscillation function not in series with the controller for selectively causing the control loop to oscillate at a tuning frequency, while the controller is in control of the process. While oscillating at the tuning frequency, a tuner is responsive to the tuning gain of the control loop and its tuning frequency for determining control parameters for tuning the controller.
U.S. Pat. No. 5,453,925 A discloses a system and method for automatically tuning a process controller used to control an industrial process, or the like, wherein the controller is removed from closed-loop control of a process under control, and a signal is applied to the process under control to cause the process to undergo controlled self-oscillation. A first portion of the self-oscillation procedure is used to determine a Time Delay characteristic of the process under control, and a subsequent portion of the self-oscillation procedure as used to calculate an Ultimate Gain characteristic and an Ultimate Period characteristic of the process under control. These three characteristics are then used to calculate control parameters which are used to tune the controller.
WO 8300753 A1 discloses a method and apparatus in tuning a PID regulator, where the process and the regulator has a transfer function G(s) in common, a method is proposed for bringing the system into self-oscillation for measuring the amplitude and frequency of the oscillation and tuning the regulator in dependence of the measurements obtained. A circuit function (NL) having non-linear characteristic and a describing function N(A) is introduced into the system in series to the process for acting on the regulator signal. Self-oscillation is obtained if (G(i omega)·N(A)=−1 for at least one value of the angular frequency omega and the amplitude A of the regulator signal.
The publication “Relay-based PID tuning” by David I. Wilson, Automation and Control, February/March 2005 discloses a method to tune parameters of a PID controller. Thereby, a relay with amplitude d is replaced for the PID controller usually controlling a plant or process. The system is then started and the plant output amplitude “a” and period “P” is recorded. From the recorded or measured amplitude “a” and period “P” eventually, the ultimate gain is calculated and the ultimate period is obtained. From the ultimate gain and period, the PID tuning parameters are found. This method may require user input of particular operational parameters.